Method for performing terminal-based handover and device therefor

ABSTRACT

Provided are a method and a device for performing a UE-based handover in a next generation wireless access network. The method of a UE may include receiving, from a source base station, an upper layer signaling including information on UE-based handover command and information on conditions for handover execution; storing a target cell configuration by using the information on conditions for handover execution; and determining whether to perform a handover procedure to a target cell, by determining whether predetermined conditions for handover are satisfied.

TECHNICAL FIELD

The present disclosure relates to methods and devices for performing aterminal-based handover (e.g., UE-based handover) in a next generationradio access network.

BACKGROUND ART

There have been many studies on next generation mobile communicationtechnologies for processing a large amount of data at a high-speed. Forexample, mobile communication systems have been developed by employingtechnologies related to the 3rd generation partnership project (3GPP),such as Long Term Evolution (LTE), LTE-Advanced, 5G, or the like. Suchmobile communication systems are high-speed and large-capacitycommunication systems capable of transmitting and receiving a largeamount of various data, such as video data, radio data, or the like, ata high speed.

Lately, a 5G network is introduced. Accordingly, it is essential toprovide mobility between 5G base stations. In particular, in case a 5Gbase station uses an mmWave frequency of a high-frequency band (e.g., 28GHz), it is expected that the coverage of the base station will befurther reduced due to the characteristics of the frequency. In such asituation, it is also expected that a terminal (hereinafter, referred toas “user equipment” (UE)) may move more frequently between basestations. Therefore, it is very important to provide an effectivehandover procedure to address such an issue.

Accordingly, due to frequent handovers and propagation characteristicsof the high-frequency band, it may be difficult to maintaincommunication connection between a UE and a base station during handoverprocedure. For example, the communication connection between the basestation and the UE may be disconnected in a handover procedure, when theUE moves out of coverage of the base station, when a communicationenvironment suddenly changes, or the like. Therefore, it may bedifficult to perform seamless communication with the UE.

Accordingly, there is a need for a technology for performing thehandover seamlessly and rapidly in the 5G network.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

To address such issues, in accordance with embodiments of the presentdisclosure, methods and devices are provided for enabling a UE todetermine whether to perform a handover procedure based on informationreceived from a base station, rather than enabling the base station.

Technical Solution

In accordance with one aspect of the present disclosure, a method of aUE is provided of performing a UE based handover. The method mayinclude: receiving high layer signaling including UE based handovercommand information and handover execution condition information forexecuting the UE based handover command from a source base station,storing a target cell configuration using the handover executioncondition information, and determining whether to hand over to a targetcell by evaluating whether the handover execution condition is met.

In accordance with another aspect of the present disclosure, a method ofa source base station is provided of controlling the execution of a UEbased handover. The method may include: configuring handover executioncondition information for executing a UE based handover command,transmitting first high layer signaling including the handover executioncondition information and UE based handover command information to a UE,and when the handover execution condition information is changed,transmitting, to the UE, second high layer signaling including changedhandover execution condition information and UE based handover commandinformation.

In accordance with further another aspect of the present disclosure, aUE is provided of performing a UE based handover. The UE may include: areceiver receiving high layer signaling including UE based handovercommand information and handover execution condition information forexecuting the UE based handover command from a source base station, anda controller storing a target cell configuration using the handoverexecution condition information and determining whether to hand over toa target cell by evaluating whether the handover execution condition ismet.

In accordance with yet another aspect of the present disclosure, asource base station is provided of controlling the execution of a UEbased handover. The source base station may include: a controllerconfiguring handover execution condition information for executing a UEbased handover command, and a transmitter transmitting first high layersignaling including the handover execution condition information and UEbased handover command information to a UE and, when the handoverexecution condition information is changed, transmitting, to the UE,second high layer signaling including changed handover executioncondition information and UE based handover command information.

Effects of the Invention

In accordance with embodiments of the present disclosure, a UE isenabled to effectively perform a handover procedure rapidly in the 5Gnetwork environment.

Further, in accordance with embodiments of the present disclosure, thehandover procedure is performed after the UE determines whether toperform the handover. Accordingly, it is possible to provide a seamlesscommunication service to users through a stable and rapid handoverprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams illustrating a handover procedure in theLTE network.

FIG. 2 is a diagram illustrating an example of measurement configurationinformation according to at least one embodiment of the presentdisclosure.

FIG. 3 is a flow diagram illustrating operations of a UE according toone embodiment of the present disclosure.

FIG. 4 is a flow diagram illustrating operations of the UE according toanother embodiment of the present disclosure.

FIG. 5 is a flow diagram illustrating operations of a source basestation according to at least one embodiment of the present disclosure.

FIG. 6 is a diagram illustrating a UE based handover procedure accordingto one embodiment of the present disclosure.

FIG. 7 is a diagram illustrating a UE based handover procedure accordingto another embodiment of the present disclosure.

FIG. 8 is a block diagram illustrating a configuration of the UEaccording to at least one embodiment of the present disclosure.

FIG. 9 is a block diagram illustrating a configuration of the sourcebase station according to at least one embodiment of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In adding referencenumerals to elements in each drawing, the same elements will bedesignated by the same reference numerals, if possible, although theyare shown in different drawings. Further, in the following descriptionof the present disclosure, a detailed description of known functions andconfigurations incorporated herein will be omitted when it is determinedthat the description may make the subject matter of the presentdisclosure rather unclear.

In the present disclosure, a machine type communication (MTC) terminalmay refer to a terminal supporting low cost (or low complexity), aterminal supporting coverage enhancement, or the like. The MTC terminalmay refer to a terminal supporting low cost (or low complexity), aterminal supporting coverage enhancement, and the like. The MTC terminalmay refer to a terminal classified into a predetermined category forsupporting low cost (or low complexity) and/or coverage enhancement.

In other words, the MTC terminal herein may refer to a low cost (or lowcomplexity) user equipment category/type newly defined in 3GPPRelease-13 and performing LTE-based MTC-related operations. The MTCterminal may refer to a user equipment category/type defined in orbefore 3GPP Release-12, which supports enhanced coverage in comparisonwith the typical LTE coverage or supports low power consumption. Or, theMTC device may refer to a low cost (or low complexity) user equipmentcategory/type newly defined in Release-13.

In the present disclosure, a wireless communication system is widelydeployed to provide various communication services, such as a voicecommunication service, a packet data service, etc. The wirelesscommunication system includes a user equipment (hereinafter, referred toas “UE”) and a base station (BS, or eNB). In the present disclosure, theUE is defined as a generic term referring to terminals used in wirelesscommunications. For example, the UE may be referred to, but not limitedto, a UE supporting wideband code division multiple access (WCDMA), longterm evolution (LTE), high speed packet access (HSPA), internationalmobile telecommunications (IMT)-2020 (5G or new radio), or the like, amobile station (MS) supporting the global system for mobilecommunication (GSM), a user terminal (UT), a subscriber station (SS), awireless device, or the like.

The base station or a cell generally refers to a station communicatingwith the UE. The base station or the cell is a generic term referringto, but not limited to, all of various communication service areas anddevices, such as a Node-B, an evolved Node-B (eNB), a gNode-B (gNB), alow power node (LPN), a sector, a site, various types of antennas, abase transceiver system (BTS), an access point, a point (e.g., atransmitting point, a receiving point, or a transceiving point), a relaynode, a megacell, a macrocell, a microcell, a picocell, a femtocell, aremote radio head (RRH), a radio unit (RU), and a small cell.

That is, the base station or the cell is defined as a generic termincluding, but not limited to, as well as some areas or functionscovered by a base station controller (BSC) in CDMA, a Node-B in theWCDMA, an evolved Node-B (eNB) or a sector (site) in the LTE, and thelike, all of various coverage areas, such as a megacell, a macrocell, amicrocell, a picocell, a femtocell and a relay node, RRH, RU, a smallcell communication range, or the like.

Each of the various cells is controlled by a base station. Therefore,the base station may be classified into two categories. The base stationmay be referred to 1) an apparatus that forms a correspondingcommunication service area, such as a megacell, a macrocell, amicrocell, a picocell, a femtocell, or a small cell, and provide arelated service to the corresponding communication service area or 2) acommunication service area. In the case of 1), the base station may bereferred to i) apparatuses controlled by the same entity to form acorresponding communication service area and provide a related servicewithin the corresponding communication service area or ii) apparatusesinteracting and cooperating with each other for forming thecorresponding communication service area and providing a related servicewithin the corresponding communication service area. According tocommunication schemes employed by a base station, the base station maybe referred to as an eNB, a RRH, an antenna, a RU, a low power node(LPN), a point, a transmission/reception point, a transmission point, areception point, or the like. In the case of 2), the base station may bea communication service area itself where UEs able to receive signalsfrom or transmit signals to other UEs and neighboring base stations.

Accordingly, the base station is defined as a generic term collectivelyincluding the megacell, the macrocell, the microcell, the picocell, thefemtocell, or the small cell, the RRH, the antenna, the RU, the LPN, thepoint, the eNB, the transmission/reception point, the transmissionpoint, or the reception point.

In the present disclosure, the UE and the base station are two entitiesfor performing transmission/reception used to embody the technology andtechnical spirit described in the present specification. The UE and thebase station are defined as a generic term and not limited to specificterms or words. The UE and the base station are two entities forperforming uplink or downlink transmission/reception used to embody thetechnology and technical spirit described in the present disclosure. TheUE and the base station are defined as a generic term and not limited tospecific terms or words. Herein, the uplink (hereinafter, referred to as“UL”) refers to data transmission/reception by a UE to/from a basestation, and the downlink (hereinafter, referred to as “DL”) refers todata transmission/reception by a base station to/from a UE.

Any of multiple access techniques may be applied to the wirelesscommunication system. For example, the wireless communication system mayemploy various multiple access techniques, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal frequency division multipleaccess (OFDMA), OFDM-TDMA, OFDM-FDMA, OFDM-CDMA, or the like. Anembodiment of the present disclosure may be applied to resourceallocation in as well as asynchronous wireless communication evolvinginto LTE/LTE-advanced and IMT-2020 beyond GSM, WCDMA, and HSPA,synchronous wireless communication evolving into CDMA, CDMA-2000, andUMB. The present disclosure is not construed to be limited to or limitedto a particular wireless communication field and is construed asincluding all technical fields to which the spirit of the presentdisclosure may be applied.

UL transmission and DL transmission may be performed based on i) a timedivision duplex (TDD) technique performing transmission throughdifferent time slots or ii) a frequency division duplex (FDD) techniqueperforming transmission through different frequencies.

Further, under the related standard, in some systems such as the LTEsystem or the LTE-advanced system, the UL and the DL are configuredbased on a single carrier or a pair of carriers. Fortransmitting/receiving control information, the UL and the DL may beconfigured with one or more control channels, such as a physical DLcontrol channel (PDCCH), a physical control format indicator channel(PCFICH), a physical hybrid ARQ indicator channel (PITCH), a physical UPcontrol channel (PUCCH), an enhanced physical DL control channel(EPDCCH), or the like. For transmitting/receiving data, the UL and theDL may be configured with one or more data channels, such as a physicalDL shared channel (PDSCH), a physical UL shared channel (PUSCH), or thelike.

Meanwhile, the control information may be transmitted through the EPDCCH(enhanced PDCCH or extended PDCCH).

In the present disclosure, the cell may refer to a coverage of a signaltransmitted from a transmission point or a transmission/reception point,a component carrier having the coverage of the signal transmitted fromthe transmission point or the transmission/reception point, or thetransmission/reception point itself.

A wireless communication system to which at least one embodiment isapplied may be i) a coordinated multi-point transmission/receptionsystem (CoMP system) in which two or more transmission/reception pointscooperate to transmit a signal, ii) a coordinated multi-antennatransmission system, or iii) a coordinated multi-cell communicationsystem. The CoMP system may include at least two multipletransmission/reception points and UEs.

The multiple transmission/reception points may be a base station ormacrocell (hereinafter, referred to as ‘eNB’) and at least one remoteradio head (RRH) that is connected to the eNB through an optical cableor an optical fiber and thereby controlled in a wired manner, and thathas high transmission power or low transmission power in the macrocellarea.

Hereinafter, the DL denotes communication or a communication path frommultiple transmission/reception points to a UE, or the UL denotescommunication or a communication path from the UE to the multipletransmission/reception points. In the DL, a transmitter may be a part ofmultiple transmission/reception points and a receiver may be a part ofthe UE. In the UL, a transmitter may be a part of the UE and a receivermay be a part of multiple transmission/reception points.

Hereinafter, transmission/reception of a signal through a channel suchas the PUCCH, the PUSCH, the PDCCH, or the PDSCH, may be described astransmission/reception of the channel, such as the PUCCH, the PUSCH, thePDCCH, or the PDSCH.

In addition, hereinafter, a description of transmitting or receiving aPDCCH or a description of transmitting or receiving a signal through thePDCCH may be used as meaning including transmitting or receiving anEPDCCH or transmitting or receiving a signal through the EPDCCH.

That is, a physical DL control channel described below may mean thePDCCH or the EPDCCH, or is also used as meaning including both the PDCCHand the EPDCCH.

Also, for convenience of description and ease of understanding, anEPDCCH may be applied to an embodiment described with the PDCCH, as anembodiment of the present disclosure, and the PDCCH may be also appliedto an embodiment described with the EPDCCH as an embodiment.

Meanwhile, higher layer signaling described below includes radioresource control (RRC) signaling transmitting RRC information containingan RRC parameter.

The eNB performs DL transmission to UEs. The eNB may transmit a physicalDL shared channel (PDSCH) which is a primary physical channel forunicast transmission, and a physical DL control channel (PDCCH) fortransmitting i) DL control information such as scheduling required toreceive the PDSCH and ii) scheduling approval information fortransmission through an UL data channel (for example, a physical ULshared channel (PUSCH)). Hereinafter, transmitting/receiving a signalthrough each channel may be described in such a manner that acorresponding channel is transmitted/received.

An enhanced mobile broadband (eMBB), massive machine-type communication(mMTC), and ultra-reliable and low latency communication (URLLC) areproposed as representative usage scenarios for NR having been discussedin the 3GPP recently.

In the present disclosure, a frequency, a frame, a subframe, a resource,a resource block (RB), a region, a band, a sub-band, a control channel,a data channel, a synchronization signal, various reference signals,various signals, and various messages, associated with NR may beinterpreted as meanings that were used in the past or are used in thepresent or as various meanings that will be used in the future.

For example, in the present disclosure, the LTE and the NR denotedifferent radio access technologies. The term “NR” as used herein refersto a new radio access technology under discussion in Release-15 of the3GPP. The NR may include various differences compared with the LTE, suchas a different frame structure, channel, core network technology, or thelike. The NR may additionally include wireless transmission in a highband, transmission of a large volume of data or transmission of data inhigh speed.

Hereinafter, for convenience of description and ease of understanding,typical radio access technologies are referred to as the LTE, and thenew radio access technology under discussion in the 3GPP is referred toas the NR. A base station may be an eNB employing the LTE technology ora gNB employing the NR technology, and one of the eNB and the gNB willbe used, when needed.

A cell is used as a generic term including, but not limited to, a radiopath, a radio link, a carrier, or the like, for transmitting data, andone base station may transmit/receive data using a plurality of cells. AUE may transmit/receive data using multiple cells, respective cells ofwhich are controlled by two base stations. As described below, indescribing carrier aggregation and dual connectivity, a case where aplurality of cells controlled by one base station is used may bediscussed using the carrier aggregation, and a case where a plurality ofcells controlled by two or more base stations is used may be discussedusing dual connectivity.

Embodiments of the present disclosure may be applied to any radio access(e.g., the LTE) networks and UEs, as well as next generation mobilecommunication (for example, 5G mobile communication/NR) UEs.

Hereinafter, for convenience of description, the base station may denotean eNode-B of LTE/E-UTRAN or an LTE base station. The base station maydenote i) an NR node, ii) a central unit (CU) and a distribute unit (DU)in the 5G radio network, iii) a gNodeB, or iv) an NR base station inwhich the CU and the DU form one logical entity. The base station mayalso be used as a generic term including the LTE base station and the NRbase station.

Hereinafter, with respect to the base station, discussions are conductedby focusing on a base station employing the next generation mobilecommunication technology (5G); however, the present disclosure can alsobe applied to in a case where one of a source base station and a targetbase station is a gNB, and the other is an eNB. That is, the basestation herein may be a gNB or an eNB, and there is no limitation to aspecific base station. It should be noted that hereinafter, for thepurpose of unity of description, discussions are conducted by focusingon a 5G environment in which the next generation mobile communicationtechnology (5G) is implemented; however, the present disclosure may alsobe equally applied to mobile communication technologies in the 4G orafter the 5G.

Further, the term “UE based handover” (e.g., terminal based handover) asdescribed herein is used for referring to a handover scheme in which aUE determines whether to perform a handover; however, embodiments of thepresent disclosure are not limited to a specific term. That is, itshould be understood that the UE based handover includes a conditionalhandover indicating a handover scheme in which a UE determines whetherto execute a handover, an autonomous handover of a UE, a UE handoverbased on the control of a base station, a faster handover commandinstruction, a handover indicating a handover executionrule/condition/threshold, or the like. Further, the handover isinstructed to a UE through an RRC connection reconfiguration messagewith mobility information (mobilityControlInformation). The mobilityinformation includes information for synchronization with a target cell(or a target base station). Accordingly, a reconfiguration procedureincluding a handover command may be used as an equal meaning to areconfiguration procedure including synchronization information.Accordingly, the term of the UE based handover (e.g., terminal basedhandover) may be replaced by various terms when needed.

In the LTE technology, a handover for supporting the mobility of a UE inan RRC connected mode is provided based a network control basis. Atarget base station prepares a handover according to a handover requestmessage from a source base station. For executing the handover, thetarget base station generates an RRC message to be transferred to a UE,that is, an RRCConnectionReconfiguration message including themobilityControlInformation. The target base station transmits a handoverrequest acknowledgment message to the source base station.

The handover request acknowledgment message includes a containercarrying an RRC message to be transferred to a UE. The containerincludes a new C-RNTI, a target eNB security algorithm identifier, adedicated RACH preamble, target eNB SIBS and one or more otherparameters. The RRC message is an RRC reconfiguration message includingthe mobilitycontrolInfo. Such an RRC message is generated by the targetbase station and then transferred to the UE via the source base station.The source base station performs integrity protection and ciphering onlyneeded for safely transmitting the RRC message.

When the UE receives the RRCConnectionReconfiguration message includingthe mobilityControlInformation, the UE performs synchronization with thetarget base station. Then, the UE accesses a target cell through arandom access channel (RACH).

The UE induces a target base station specific key (target eNB specifickey) and configures a selected security algorithm to be used in thetarget cell.

The UE initiates synchronization to DL of the target PCell.

The UE resets master cell group (MCG) MAC and secondary cell group (SCG)MAC, if configured.

The UE re-establishes packet data convergence protocol (PDCP) for allestablished radio bearers (RBs).

The UE re-establishes MCG radio link control (RLC) and SCG RLC, ifconfigured, for all established radio bearers (RBs).

The UE configures lower layers to consider SCell(s), if configured, tobe deactivated.

The UE applies a value of a new UE identifier (newUE-Identity) with aC-RNTI.

The UE submits, to lower layers, an RRC connection reconfigurationcomplete message for transmission to the target base station.

The target base station (eNB) responds with UL allocation and timingadvance.

When the UE successfully accesses the target cell, for confirming thehandover, the UE transmits an RRCConnectionReconfigurationCompletemessage (using the C-RNTI) for indicating that the handover for the UEhas been completed to the target base station, along with an UL bufferstatus report (BSR). The target base station verifies the C-RNTIincluded in the RRCConnectionReconfigurationComplete message.

The target base station starts to send data.

The network based handover procedure has been performed through such aprocedure. More specifically, the handover in the LTE technology isdescribed with reference to FIGS. 1A and 1B.

FIGS. 1A and 1B are diagrams illustrating a handover procedure in theLTE network.

Referring to FIGS. 1A and 1B, at step 0, a source base station 110provides an area restrictive service through a serving gateway 140. Atstep 1, the source base station 110 transmits measurement controlinformation for measurement reporting to a UE 100. The UE 100 connectedto the source base station 110 transmits packet data to a servinggateway through the source base station 110, and the UE 100 receivespacket data through the identical path. For enabling the UE 100 totransmit UL data, the source base station 110 allocates an UL resourceto the UE 100.

At step 2, the UE 100 transmits a measurement report including ameasurement result according to a measurement reporting trigger to thesource base station 110. Thereafter, at step 3, the source base station110 determines a handover of the UE 100 based on the measurement report.

When the handover of the UE 100 is determined, at step 4, the sourcebase station 110 transmits a handover request message for enabling theUE to prepare the handover to a target base station 120. At step 5, thetarget base station 120 determines whether to admit a requestedresource, and the target base station 120 generates configurationinformation to be transmitted to the UE. At step 6, the target basestation 120 transmits a handover request acknowledgment messageincluding configuration information to be configured in the UE 100,which is contained in a container, to the source base station 110. Thiscontainer is a transparent container transferred to the UE as an RRCconnection reconfiguration message for enabling the UE to perform thehandover. For example, the transparent container may be set such that anintermediate entity forwards the container without changing the contentsof the container.

To transmit the configuration information for the handover to the UE100, the source base station 110 allocates a DL resource to the UE andtransmits, to the UE, the RRC connection reconfiguration message, whichis the container received from the target base station 120, at step 7

The UE 100 calculates a pre-allocated UL resource and the source basestation 110 buffers packets to be transferred to the target base station120.

In the process of the handover, the UE 100 and the source base station110 transmits and receives packet data, and the source base station 110transmits a SN statue transfer message to the target base station 120 atstep 8. The source base station 110 forwards the data to the target basestation 120.

The UE 100 performs a synchronization procedure to synchronize to a cellof the target base station 120 at step 9. The target base station 120buffers the data forwarded from the source base station 110.

At step 10 a, the target base station 120 may allocate periodic ULresources to the UE, and provide UL resource allocation and TA for theUE 100 at step 10. Through these procedures, after the UE 100 hassynchronized to the target base station 120, accessed the target basestation through a random access procedure, and completed the handover,the UE transmits an RRC connection reconfiguration complete message tothe target base station 120 at step 11. Thereafter, the UE 100 transmitsand receives packet data to a serving gateway 140 via the target basestation 120.

At steps 12 and 13, the target base station 120 requests data pathswitch to an MME 130, and the MME 130 transmits a bearer modificationrequest message to the serving gateway 140. At step 14, the servinggateway 140 switches a DL data path. To do this, a target marker may betransferred to the target base station 120 via the source base station110. Packet data may be transmitted and received between the servinggateway 140 and the target base station 120.

When the bearer modification is completed, the serving gateway 140transmits a bearer modification complete message to the MME 130 at step15. At step 16, the MME 130 transmits an acknowledgment messagenotifying that the data path switch request has been completed to thetarget base station 120.

Thereafter, at step 17, the target base station 120 indicates UE contextrelease to the source base station 110. Finally, at step 18, the sourcebase station 110 releases the UE context, and then the handoverprocedure is completed.

Like this, the network control based handover is performed well in thetypical radio environment as a basic handover method. However, in caseradio quality of a serving cell is changed suddenly, there has been apossibility that a handover may fail as a UE does not receive a handovercommand or receives it too late. In particular, radio link quality maybe degraded faster in an NR (5G) radio network employing a highfrequency band and a beam-based system. In this case, as the UE movesbeyond a current serving beam coverage area, there has been apossibility that the UE may not receive RRC signaling via a servingnode.

To address such issues, in accordance with embodiments of the presentdisclosure, a UE based handover is provided, in which a UE directlydetermines whether to perform a handover procedure and perform thehandover procedure based on the determination.

Further, in the procedure of the UE based handover, when the target basestation allocates a resource (a RACH preamble, a C-RNTI, or the like)for a corresponding UE and includes the allocated resources in ahandover command, the radio resources cannot be used or releasedefficiently. In addition to this, the UE based handover may use athreshold value lower than a typical threshold value for instructingmeasurement configuration in order to provide related configurationinformation to the UE faster. As an alternative, to execute efficientlythe UE based handover, the UE based handover may be configured for oneor more candidate cells. To do this, more number of measurementconfigurations may be instructed. Like this, the UE based handover maygenerate more measure reports than the typical handover because of acomparatively lower threshold value. As a result, signaling overhead mayincrease.

Accordingly, proposed herein is a UE based handover procedure foreffectively utilizing resources of a target base station and preventingsignaling overhead.

As described above, embodiments will be discussed by focusing on ahandover of an NR radio new radio, but may be applicable to a handoverin any other radio network or system, as well as the LTE. Further,embodiments may be applicable to a handover between an NR radio networkand an LTE network connected to a 5G core network system, and beapplicable to a handover between an NR radio network and an LTE networkconnected to an EPC. Similarly, the embodiments may be applicable to ahandover between an NR radio network and an LTE network connected torespective core networks.

A base station may instruct measurement configuration to an RRCconnected UE equally in both the network based handover and the UE basedhandover. A physical layer in the UE performs measurement and thentransfers the measured data to an RRC layer. The physical layer mayperform L1 filtering. When the measured data is transferred from thephysical layer, the RRC layer performs L3 filtering according to themeasurement configuration. After the L3 filtering, the filtered data areused for evaluating a reporting criterion. The reporting criterionaccording to the measurement configuration is used to determine whetherto trigger reporting.

When the reporting is triggered, the UE reports the measured resultaccording to the measurement configuration to the base station.

FIG. 2 is a diagram illustrating an example of measurement configurationinformation according to at least one embodiment of the presentdisclosure.

Referring to FIG. 2, a measurement configuration using an RRC messagemay include the following parameters.

A measurement object is defined as an object measured by a UE, such as afrequency or a cell. In the LTE, a single measurement object isconfigured for a given frequency. With respect to heterogeneous RATmeasurement, a measurement object for the UTRA is configured with a setof cells for a single frequency. A measurement object for the GERAN isconfigured with a set of carrier frequencies.

A reporting configuration indicates a reporting criterion and areporting format. The reporting criterion (trigger type) denotes acriterion for triggering a UE to transmit a measurement report, and thereporting format denotes measurement quantities included in themeasurement report. The reporting may be triggered periodically ortriggered based on a predetermined event. In addition to this, the UEmay transmit periodic reports to a base station based on thepredetermined event after the reporting has been triggered. This may beconfigured through a number and an interval of the measurement reportsin the reporting configuration.

Thus, for the UE based handover, the UE is required to performmeasurement operation for measuring the quality of a radio network. Todo this, a base station may provide a measurement configuration to theUE.

Hereinafter, operations of a UE and a base station performing the UEbased handover will be discussed with reference to the accompanyingdrawings.

FIG. 3 is a flow diagram illustrating operation of a UE according toembodiments of the present disclosure.

Referring to FIG. 3, a UE may receive high layer signaling including UEbased handover command information and handover execution conditioninformation for executing the UE based handover from a source basestation, at step S310.

For example, the UE may receive execution condition informationincluding handover command information and condition information forexecuting the handover from a source base station having an RRCconnection with the UE. For example, the handover execution conditioninformation and the handover command information may be included in anRRC connection reconfiguration message.

The handover execution condition information may be configured by atarget base station and then transferred to the source base station. Asanother example, the handover execution condition information may beconfigured by the source base station. As a further another example, thehandover execution condition information may be configured by the targetbase station and then transferred to the UE via the source base station.As a yet another example, the handover execution condition informationmay be configured by the source base station and transferred to thetarget base station, and then, the target base station may transfer itto the UE via the source base station. For example, the handoverexecution condition information may include a timer for indicating avalidity period of the handover command or handover execution conditioninformation. As an example, when the timer expires, the handover commandor handover execution condition information may be considered asinvalid.

In addition, the handover execution condition information may includeinformation, parameters, timers and the like, needed for performingvarious embodiments or examples described below. As an example, thehandover execution condition information may include at least one ofparameter information for channel quality measurement needed forperforming the UE based handover, trigger condition information forreporting a measured result, a timer for restricting or suppressingmeasurement reporting, a timer for indicating the validity period,indication information indicating a UE based handover command and UEconfiguration information for accessing a target base station. As anexample, the UE configuration information may include a C-RNTI appliedin a target base station, a target base station security algorithmidentifier, a target base station dedicated RACH preamble, target basestation SIB information, and the like. As another example, the parameterinformation for the channel quality measurement may include, asmeasurement object information, frequency information, reference signalconfiguration information, threshold value information, frequency offsetinformation, cell list information, and a measurement identifier. As afurther another example, the trigger condition information for reportinga measured result may include a condition/rule/event threshold value,and condition/rule/event offset information.

The handover execution condition information or the handover commandinformation may be configured for each of a plurality of target basestations or a plurality of target cells. That is, the high layersignaling may include a plurality of handover execution conditioninformation or handover command information, each of which may beincluded in a container for each identifier or for each target cell ortarget base station. The corresponding identifier may be associated withinformation on a measurement object, a measurement identifier, or atarget cell identifier, included in a measurement configuration.

Thereafter, the UE may store a target cell configuration using thehandover execution condition information, at step S320. For example,when UE based handover command information and handover executioncondition information are received, the UE verifies whether the UE basedhandover has been instructed and store the target cell configurationaccording to the handover execution condition information.

For example, the UE stores a measurement configuration for measuringchannel quality of the target cell according to the handover executioncondition information and stores a trigger event, a trigger condition,or the like applied to the target cell.

As another example, when UE configuration information included in thehandover execution condition information is stored and a handover to atarget base station is determined, the UE is allowed to access rapidlythe target base station without separately receiving a configuration ofthe target base station.

Meanwhile, as described above, when the handover execution conditioninformation includes a timer for indicating a validity period (orrestricting the applying of the validity period) of handover commandinformation or handover execution condition information, the UE verifieswhether the timer expires. When the timer expires, the UE releases thestored target cell configuration. Through this, it is possible toprevent resources from wasting, which is caused by continually occupyingUE configuration information allocated or to be allocated by the targetbase station for the UE.

The UE may evaluate whether the handover execution condition informationis met and determine whether to hand over to the target cell, at stepS330. For example, the UE monitors channel quality of the target cellbased on the stored target cell configuration and determine whether toperform the handover using the monitored result without a separateindication by the source base station.

For example, when a trigger condition included in the handover executioncondition information is met, the UE determines handover execution tothe target base station controlling the corresponding target cell.

As another example, the UE may not report a measurement result for thetarget base station to the source base station when the handoverexecution is determined. That is, when the UE based handover isconfigured, the UE controls a measurement result meeting a handoverexecution condition not to be transmitted to the source base station. Asan alternative, when the UE based handover is configured, the UEcontrols measurement reporting not to be transmitted to the source basestation until the timer of the validity period expires. In the situationthat the source base station has instructed the handover command, thisprovides an effect of reducing one or more related procedure(s) or theentire load of the system caused by unnecessary measurement reportingrepetition.

When handover execution is triggered to the target base station, the UEperforms a random access procedure and access the target base stationusing the UE configuration information described above. Thus, sinceseparate indication information from the source base station is notneeded to be received, it is possible to prevent the handover from beinginterrupted even when the radio environment is changed suddenly.

FIG. 4 is a flow diagram illustrating operations of the UE according toanother embodiment of the present disclosure.

Referring to FIG. 4, as discussed with reference to FIG. 3, the UE mayreceive high layer signaling including UE based handover commandinformation and handover execution condition information, at step S410.The operation of step 410 is similar to the operation of step S310.

Thereafter, the UE may store a target cell configuration received atstep S410, at step S420. The operation of step 420 is similar to theoperation of step S320.

After the UE has stored the target cell configuration, a source basestation may change a UE based handover of the UE, or change a targetcell or a target base station.

In this case, after the high layer signaling including the UE basedhandover command information has been received, in case the UE does notchange the target cell or the target base station and maintains theconnection with the source base station, due to not meeting a UE basedhandover criterion, the UE may receive second high layer signalingincluding other UE based handover command information, at step S430. Forexample, through a message identical to the high layer signalingreceived at step S410, the UE may receive handover command informationor handover execution condition information different from the handovercommand information or the handover execution condition information atstep S410. Herein, the second high layer signaling is used todistinguish from the high layer signaling at step S410, which may bereferred to as first high layer signaling.

When the second high layer signaling is received, the UE may change thestored target cell configuration to a second target cell configurationconfigured using handover execution condition information included inthe second high layer signaling, at step S440. For example, the UE mayreplace the target cell configuration stored at step S420 with theinformation included in the second high layer signaling. Herein, thesecond target cell configuration is used to distinguish from the targetcell configuration at step S420, which may be referred to as a firsttarget cell configuration.

The second target cell configuration may include UE configurationinformation of a target base station as described above. When the sourcebase station changes the target cell or the target base station, thefirst target cell configuration is released or deleted, and the secondtarget cell configuration may be newly stored.

As an alternative, when handover command or handover execution conditioninformation included in the second high layer signaling indicates ahandover scheme defined in the LTE other than the UE based handover, thefirst target cell configuration is deleted, and the handover defined inthe LTE may be executed. That is, when the UE based handover iscanceled, the UE may delete or replace the first target cellconfiguration for executing handover operations according to the typicalscheme.

When the first target cell configuration is changed while maintainingthe UE based handover, the UE may determine whether to execute thehandover using the second target cell configuration, at step S450. Whenhandover execution is determined because the received handover executioncondition is satisfied, the UE may perform a procedure of accessing thechanged target base station.

Through this, the source base station dynamically may change or controlthe UE based handover.

The operations of the UE described above will be discussed again withrespective to a source base station.

FIG. 5 is a flow diagram illustrating operations of a source basestation according to at least one embodiment of the present disclosure.

Referring to FIG. 5, the source base station may configure (e.g.,generate) handover execution condition information for performing a UEbased handover command, at step S510.

For example, the handover execution condition information may beconfigured by the source base station or be configured by the sourcebase station after the source base station has received information froma target base station. As an alternative, the source base stationreceives information to be included in the handover execution conditioninformation from a target base station and then generates the handoverexecution condition information to be transmitted to the UE.

For example, the handover execution condition information may include atimer for indicating a validity period of the handover command orhandover execution condition information. For example, when the timerexpires, the handover command or handover execution conditioninformation may be considered as invalid.

In addition to this, the handover execution condition information mayinclude information, parameters, timers and the like, needed forperforming various embodiments or examples described below. As anexample, the handover execution condition information may include atleast one of parameter information for channel quality measurementneeded for performing the UE based handover, trigger conditioninformation for reporting a measured result, a timer for restricting orsuppressing measurement reporting, a timer for indicating the validityperiod, indication information indicating a UE based handover commandand UE configuration information for accessing a target base station.For example, the UE configuration information may include a C-RNTIapplied in a target base station, a target base station securityalgorithm identifier, a target base station dedicated RACH preamble,target base station SIB information, and the like.

The handover execution condition information or the handover commandinformation may be configured for each of a plurality of target basestations or a plurality of target cells. That is, the source basestation may configure a plurality of handover execution conditioninformation or handover command information, each of which may beincluded in a container for each identifier or for each target cell ortarget base station.

The source base station may transmit, to a UE, high layer signalingincluding the handover execution condition information and the UE basedhandover command information, at step S520. For example, the source basestation may transmit execution condition information including handovercommand information and condition information for executing the handovercommand to a UE having an RRC connection with the source base station.For example, the handover execution condition information and thehandover command information may be included in an RRC connectionreconfiguration message and transmitted to the UE. Further, the highlayer signaling may include a plurality of handover execution conditioninformation or handover command information, each of which may beincluded in a container for each identifier or for each target cell ortarget base station.

The UE may verify the high layer signaling received from the source basestation and store a target cell configuration using the handoverexecution condition information. When a timer indicating the validityperiod is included in the handover execution condition information, theUE may release the target cell configuration when the timer expires.

When the handover execution condition information is changed, the sourcebase station may transmit, to the UE, second high layer signalingincluding changed handover execution condition information and UE basedhandover command information, at step S530. As discussed with referenceto FIG. 4, the handover command or handover execution conditioninformation may be changed by the source base station.

For example, the source base station may change to a network basedhandover, such as the LTE handover procedure, after the UE basedhandover command has been transmitted. As an alternative, the sourcebase station may change a target base station after a command of the UEbased handover to a specific target base station has been transmitted.In this case, the source base station transmits second high layersignaling including changed handover execution condition information andhandover command information to the UE

When the second high layer signaling is received, the UE may replace theearlier stored target cell configuration with a second target cellconfiguration using the handover command information and the handoverexecution condition information in the second high layer signaling. Todo this, the UE may release or delete the earlier stored target cellconfiguration and newly store the second target cell configurationaccording to the second high layer signaling. As an alternative, the UEmay modify a target cell configuration for a target cell identical tothe earlier stored target cell to become the second target cellconfiguration according to the second high layer signaling.

Thereafter, the UE determines whether to hand over from the source cellto the target cell by evaluating whether the handover executioncondition is met. When the handover is triggered according to thehandover execution condition information, the UE may control ameasurement result for the target cell not to be transmitted to thesource base station.

Hereinafter, embodiments for instructing a measurement configuration toa UE for performing a UE based handover will be described in detail.Further, embodiments for providing high layer signaling includinghandover execution condition indication to the UE for performing the UEbased handover will be described in detail. A timer, indicationinformation, restriction information, suppression information, ameasurement configuration, a UE configuration, or the like describedbelow denotes information or a parameter included in the UE basedhandover execution condition information described above.

First, embodiments of performing a measurement configuration by a sourcebase station for a UE based handover for a UE will be described.

A network may instruct the UE based handover to the UE. As an example,the source base station may request the UE based handover to a targetbase station, receive UE configuration information for the UE basedhandover generated by the target base station, and then provide thereceived information to the UE. As another example, without requestingthe UE based handover to the target base station and receiving UEconfiguration information for the UE based handover generated by thetarget base station in response to the request, the source base stationmay instruct a UE based handover configuration to the UE according to adetermination of the source base station. As further another example,the source base station may transfer handover execution conditioninformation for requesting the UE based handover to the target basestation, receive UE configuration information for the UE based handovergenerated by the target base station, and then indicate the receivedinformation to the UE.

As described above, in the UE based handover, to provide relatedconfiguration information to the UE faster, a measurement configurationmay be instructed using a lower threshold value than the typicalhandover. As an alternative, to execute efficiently the UE basedhandover, the UE based handover may be configured for one or morecandidate target cells. To do this, more number of measurementconfigurations may be instructed. Like this, the UE based handover maycause to generate more measurement reports due to a comparatively lowerthreshold value that causes faster handover triggering, or the like.

Hereinafter, embodiments of measurement configuration for the UE basedhandover will be described. Embodiments described below may be performedindividually or in combination with one or more of embodiments orexamples.

Embodiments of a prohibition/suppression timer for enabling a sourcebase station to restrict measurement reporting

The source base station may provide, to a UE, a prohibition/suppressiontimer (hereinafter, for convenience of description, referred to as theprohibition timer) for restricting measurement reporting. For example,the prohibition timer may be included in the handover executioncondition information described above.

The prohibition/suppression timer is provided for the measurementreporting. For example, the prohibition/suppression timer may be appliedfor a specific event or a specific event group. As another example, theprohibition/suppression may be applied for an entire reportingconfiguration. As further another example, this may be applied forentire event reporting.

As an example, when the prohibition timer is running, the UE mayprohibit, suppress, or delay the measurement reporting.

As another example, in case a base station instructs the UE to performthe UE based handover; in case the UE based handover is configured; whenthe UE based handover is instructed and then applied; or in case an RRCmessage including a UE configuration for the UE based handover isreceived, the UE starts or restarts the prohibition timer by setting itas a value indicated by the base station.

As another example, in case the prohibition timer is indicated (e.g.,instructed or provided) by the base station, the UE sets the prohibitiontimer as a value indicated by the base station and starts or restartsit.

As another example, in case the prohibition timer is indicated by thebase station, when initiating a measurement reporting procedure, the UEsets the prohibition timer as a value indicated by the base station andstarts or restarts it.

As another example, in case the prohibition timer is indicated by thebase station, when transmitting measurement reporting to the basestation, the UE sets the prohibition timer as a value indicated by thebase station and starts or restarts it.

As another example, in case the prohibition timer is indicated by thebase station, when transmitting first measurement reporting for acorresponding event to the base station, the UE sets the prohibitiontimer as a value indicated by the base station and starts or restartsit.

As another example, in case the prohibition timer is indicated by thebase station, when transmitting measurement reporting for acorresponding event to the base station, the UE sets the prohibitiontimer as a value indicated by the base station and starts or restartsit.

As another example, in case measurement reporting of the UE isprohibited/suppressed/delayed according to the prohibition timer, the UEmay store measurement results or measurement reporting.

As another example, in case measurement reporting of the UE isprohibited/suppressed/delayed according to the prohibition timer, the UEmay discard/release/stop corresponding measurement results ormeasurement reporting.

As another example, in case measurement reporting of the UE isprohibited/suppressed/delayed according to the prohibition timer, the UEmay suspend/stop corresponding measurement.

As another example, when the prohibition timer expires, the UE transmitsmeasurement reporting. For example, the UE transmits stored measurementresults or measurement reporting. As an alternative, the UE transmitsmeasurement results or measurement reporting at a current time when thetimer expires.

The prohibition timer for restricting measurement reporting may beinstructed to the UE along with information (e.g., handover commandinformation, or handover execution condition information) indicating theUE based handover. As another example, the prohibition timer may beactivated when information indicating a UE based handover is configured.

The UE receiving information indicating a UE based handover may performone or more of the following operations.

The UE maintains a connection with a source cell (e.g., a source basestation). The UE may request scheduling to the source cell, or thescheduling may be indicated to the UE.

The UE stores a target cell configuration (e.g., a UE configuration/RRCcontext/RRC IE/L1, L2 configuration information) information forexecuting the handover to a target cell.

The UE monitors a trigger condition (e.g., a rule, a regulation, or anevent) for determining handover execution.

Embodiments of a prohibition/suppression timer for enabling a targetbase station to control measurement reporting

A target base station may instruct a prohibition timer for restrictingmeasurement reporting to a UE. To do this, the target base station maytransfer an RRC message including handover execution conditioninformation (e.g., including UE configuration information) forinstructing the UE based handover to the UE via a source base station.

The UE receiving information instructing a UE based handover may performone or more of the following operations.

The UE maintains a connection with a source cell (e.g., the source basestation). The UE may request scheduling to the source cell, or thescheduling may be indicated to the UE.

The UE stores a target cell configuration (e.g., a UE configuration/RRCcontext/RRC IE/L1, L2 configuration information) information forexecuting the handover to a target cell.

The UE monitors a trigger condition (e.g., a rule, a regulation, or anevent) for determining handover execution.

The prohibition/suppression timer is for the measurement reporting. Asan example, the prohibition/suppression timer may be applied for aspecific event or a specific event group. As another example, theprohibition/suppression timer may be applied for an entire reportingconfiguration. As further another example, the prohibition/suppressiontimer may be applied for entire event reporting.

As an example, when the prohibition timer is enabled or running, the UEmay prohibit, suppress, or delay the measurement reporting.

As another example, in case a base station instructs the UE to performthe UE based handover; in case the UE based handover is configured; whenthe UE based handover is instructed and then applied; or in case an RRCmessage including a UE configuration for the UE based handover isreceived, the UE starts or restarts the prohibition timer by setting itas a value indicated by the base station.

As another example, in case the prohibition timer is indicated (e.g.,provided or instructed) by the base station, the UE sets the prohibitiontimer as a value indicated by the base station and starts or restartsit.

As another example, in case the prohibition timer is indicated by thebase station, when initiating a measurement reporting procedure, the UEsets the prohibition timer as a value indicated by the base station andstarts or restarts it.

As another example, in case the prohibition timer is indicated by thebase station, when transmitting measurement reporting to the basestation, the UE sets the prohibition timer as a value indicated by thebase station and starts or restarts it.

As another example, in case the prohibition timer is indicated by thebase station, when transmitting first measurement reporting for acorresponding event to the base station, the UE sets the prohibitiontimer as a value indicated by the base station and starts or restartsit.

As another example, in case the prohibition timer is indicated by thebase station, when transmitting measurement reporting for acorresponding event to the base station, the UE sets the prohibitiontimer as a value indicated by the base station and starts or restartsit.

In case measurement reporting of the UE is prohibited/suppressed/delayedaccording to the prohibition timer, the UE may store measurement resultsor measurement reporting.

As another example, in case measurement reporting of the UE isprohibited/suppressed/delayed according to the prohibition timer, the UEmay discard/release/stop corresponding measurement results ormeasurement reporting.

As another example, in case measurement reporting of the UE isprohibited/suppressed/delayed according to the prohibition timer, the UEmay suspend/stop corresponding measurement.

When the prohibition timer expires, the UE may transmit measurementreporting. As an example, the UE may transmit stored measurement resultsor measurement reporting. As another example, the UE may transmitmeasurement results or measurement reporting at a current time when theprohibition timer expires.

Embodiments of indicating prohibition/suppression indication informationfor enabling a source base station or a target base station to restrictmeasurement reporting

A source base station or a target base station may indicate (e.g.,provide) prohibition/suppression indication information for restrictingmeasurement reporting to a UE. As an example, the source base stationmay transfer, to the UE, an RRC message including UE configurationinformation for indicating the UE based handover. As another example, todo this, the target base station may transfer an RRC message includingUE configuration information for indicating the UE based handover to theUE via the source base station.

As further another example, to do this, the source base station maytransfer UE configuration information for indicating the UE basedhandover to target base station, and the target base station maytransfer an RRC message including the UE configuration information forindicating the UE based handover the UE via the source base station.

The UE receiving information indicating a UE based handover may performone or more of the following operations.

The UE maintains a connection with a source cell. The UE may requestscheduling to the source cell, or the scheduling may be indicated to theUE.

The UE applies configuration information for handover execution to thesource cell.

The UE stores a target cell configuration (e.g., a UE configuration/RRCcontext/RRC IE/L1, L2 configuration information) information forexecuting the handover to a target cell.

The UE monitors a trigger condition (e.g., a rule, a regulation, or anevent) for determining handover execution.

Even when a reporting condition/event is satisfied based on themonitoring results for the condition/event for determining (e.g.,triggering) handover execution, the UE may not trigger or transfermeasurement reporting.

Even when a reporting condition is satisfied based on the monitoringresults of the condition/event for determining handover execution, theUE may prohibit/suppress triggering/transferring measurement reporting.

The prohibition/suppression indication information representsinformation for indicating prohibition/suppression/restriction for themeasurement reporting. As an example, the prohibition/suppressionindication information may be applied for a specific event or a specificevent group. As another example, the prohibition/suppression indicationinformation may be applied for an entire reporting configuration. Asfurther another example, the prohibition/suppression indicationinformation may be applied for entire event reporting.

For example, when the prohibition indication information is provided tothe UE, configured in the UE, or enabled or running, the UE mayprohibit/suppress/delay the measurement reporting.

As further another example, in case a base station instructs the UE toperform the UE based handover; in case the UE based handover isconfigured in the UE; when the UE based handover is instructed and thenapplied in the UE; or in case the UE receives an RRC message including aUE configuration for the UE based handover, the UE may restrictinitiation or transfer of reporting or measurement reporting accordingto RRM measurement or RRM measurement evaluation. As an alternative, theUE may not perform one or more of the trigger/transfer/initiation ofreporting or measurement reporting according to the RRM measurement orthe RRM measurement evaluation.

As methods described above, the base station may perform controloperations for restricting measurement reporting of the UE, and the UEmay restrict measurement reporting according to corresponding controloperations as well. Hereinafter, embodiments of enabling a base stationto control the UE based handover will be discussed.

An example of enabling a source base station or a target base station toprovide (e.g., instruct) a validity period/timer/time value forrestricting the UE based handover.

A source base station or a target base station may provide a validityperiod/timer/time value for restricting the UE based handover. Thevalidity period/timer/time value may be included in the handoverexecution condition information described above.

In the typical technology, when one or more cells satisfy an eventtriggering condition, the UE triggers an event for reporting measurementresults of one or more cells in a measurement report message. When theprohibition timer for restricting the UE based handover, the prohibitionindication information for restricting the UE based handover, or thevalidity period/timer/time value for restricting the UE based handoveris indicated, the UE may perform one or more of the following operationsbased on the indicated information.

The UE maintains a connection with a source cell. The UE may requestscheduling to the source cell, or the scheduling may be indicated to theUE.

The UE applies configuration information for handover execution to thesource cell.

The UE sets a specific timer for restricting the UE based handover as avalidity period/timer/time value indicated (e.g., instructed orprovided) by a base station, and then starts or restarts it.

The UE stores a UE configuration/RRC context/RRC IE/L1, L2 configurationinformation for executing a handover to a target cell.

The UE performs measurement for a condition/event for determininghandover execution.

Even when a reporting condition/event is satisfied based on themeasurement results for the condition/event for determining handoverexecution, the UE may control measurement reporting not to betriggered/transferred/initiated.

Even when a reporting condition/event is satisfied based on themeasurement results of the condition/event for determining handoverexecution, the UE may prohibit/suppress the trigger/transfer/initiationof measurement reporting.

As an example, the embodiment may be applied for a specific event or aspecific event group. As another example, the embodiment may be appliedfor an entire reporting configuration. As further another example, theembodiment may be applied for entire event reporting.

As an example, when a specific timer for restricting the UE basedhandover is indicated, configured, enabled, or run, the UE measures acondition/event for determining handover execution. When thecondition/event is satisfied, the UE may perform UE based handoverexecution. For example, the UE may perform one or more of initiatingrandom access, performing synchronization, applying UE configurationinformation, and transmitting a handover complete message to a targetcell.

As another example, in case a base station instructs the UE to performthe UE based handover; in case the UE based handover is configured inthe UE; when the UE based handover is instructed and then applied in theUE; or in case the UE receives an RRC message including a UEconfiguration for the UE based handover, the UE mayprohibit/suppress/restrict the trigger of reporting or measurementreporting according to RRM measurement or RRM measurement evaluation. Asan alternative, the UE may not perform one or more of thetrigger/transfer/initiation of reporting or measurement reportingaccording to the RRM measurement or the RRM measurement evaluation. Asan alternative, the UE measures a condition/event for determininghandover execution, and when the condition/event is satisfied, the UEmay initiate/perform UE based handover execution. For example, the UEmay perform one or more of initiating random access, performingsynchronization, applying UE configuration information, and transmittinga handover complete message to a target cell.

As another example, when a specific timer for restricting the UE basedhandover expires, the UE may release or discard a condition/event for UEbased handover execution or UE configuration information for UE basedhandover execution.

As further another example, in the UE based handover, the UE occupies atarget base station resource until the UE determines handover execution.However, it is undesirable for this situation to persist for a longtime. Accordingly, the target base station may indicate (e.g., provideor instruct) information for restricting the UE based handover execution(a maximum waiting time). For example, to do this, a timer value may beprovided. The timer value may be included in the handover executioncondition information. The UE receiving information instructing the UEbased handover starts a timer for restricting the UE based handoverexecution (a maximum waiting time). As an example, when the UE basedhandover execution is triggered or determined, the UE may stop thecorresponding timer. As another example, when the corresponding timerexpires before the UE based handover execution is triggered ordetermined, the UE may stop a condition/event for the handover. Asfurther another example, when the corresponding timer expires before theUE based handover execution is triggered or determined, handoverexecution condition information (including UE configuration information)for performing handover execution may be released.

As described above, the UE receives information for restrictingmeasurement reporting and information for restricting UE based handoverexecution. As results, the UE may perform a measurement reportingoperation, a UE based handover operation, a handover execution conditioninformation release operation, or the like.

Hereinafter, various embodiments for enabling a base station to instructa UE based handover command to a UE will be described. Informationdescribed below may be included in the UE based handover commandinformation or the handover execution condition information describedabove.

For an RRC connected UE, the base station is required to correctlyrecognize capabilities of the UE to provide a configuration suitable forthe UE. A core network control entity of the UE stores UE capabilitiesincluding a UE radio access capability and a UE core network capability.

For example, the UE core network capability may be provided by the UEthrough NAS signaling (attach procedure, etc.). As another example, theUE radio access capability may be transferred from the UE to the basestation using a UE capability transfer procedure and transferred to thecore network control entity via an interface between the base stationand the core network control entity. When the base station transmits aUE capability enquiry message to the UE, the base station may receive UEcapability information by replying of the UE to this through UEcapability information.

As further another example, the UE radio access capability may beprovided to the core network control entity by the UE through NASsignaling (attach procedure, etc.), and transferred to the base stationvia the interface between the base station and the core network controlentity.

The core network control entity may transmit the UE radio accesscapability to the base station whenever the UE enters an RRC connectionstate.

The UE may provide UE capability information representing a UE basedhandover capability to the base station. The UE capability informationmay represent a capability for each specific band or for each specificband combination, or represent a capability irrespective of the band.That is, the base station may verify whether the UE is available toexecute the UE based handover through the UE capability information.

Meanwhile, the network may instruct (e.g., provide) a measurementconfiguration and a measurement reporting configuration to the UE. Basedon this, the measurement reporting may be received.

For example, the network (e.g., base station) may instruct (e.g.,provide) a UE based handover configuration based on the measurementreporting to the UE. The base station may determine whether to instructa UE based handover command to the UE by receiving at least one of theUE capability information and the measurement report.

Meanwhile, cooperation between a source base station and a target basestation may be required to perform the UE based handover. Relatedembodiments will be described below, and the following embodiments maybe applicable individually or in combination with one or moreembodiments or examples.

An Embodiment of Enabling a Source Base Station to Transmit UE BasedHandover (Request) Indication Information to a Target Base Station

As described above, in the typical handover technology, a target basestation allocates a new C-RNTI, a dedicated RACH preamble, or the liketo be used in a UE according to a handover request of a source basestation. In the case of applying the UE based handover, there is apossibility that one or more resource(s) allocated by the target basestation may not be used for a certain period until a handover isexecuted. If the target base station has a heavy load, it may bedesirable not to allow a UE based handover before the target basestation generates such a configuration. Further, if needed, it may bedesirable for the target base station to recognize that a correspondinghandover is the UE based handover during waiting for the execution ofthe UE based handover. In addition to this, when the target base stationdoes not support a UE based handover functionality, there may be a needfor enabling the target base station to response taking into thisaccount.

Accordingly, before a source base station commands the UE based handoverto a UE, a procedure may be needed for reflecting a situation of thetarget base station by transmitting a request or indication informationrelated to the UE based handover to the target base station.

For example, when the source base station determines the UE basedhandover, the source base station may include information for indicatingthe UE based handover (or information for requesting the UE basedhandover, or condition information for the UE based handover, forconvenience of description and ease of understanding, hereinafter, maybe referred to as “information for indicating the UE based handover”) ina handover request message. Then, the source base station may transmitthe handover request message including the information for indicatingthe UE based handover to the target base station,

As another example, when the source base station determines the UE basedhandover, the source base station may include information for indicatingthe UE based handover in a handover preparation message included in thehandover request message and then transmit the message including theinformation to the target base station.

As further another example, to receive help information for determiningthe UE based handover from the target base station, the source basestation may include the information for indicating the UE based handoverin the handover request message (e.g., set to true) and then transmitthe message including the information to the target base station.

As yet another example, to receive help information for determining theUE based handover from the target base station, the source base stationmay include the information for indicating the UE based handover in ahandover preparation message included in the handover request messageand then transmit the message including the information to the targetbase station.

Hereinafter, embodiments of operations of a target base station thatreceives information for requesting the corresponding UE based handoverwill be described.

A Method of Handling a UE Based Handover when the Target Base Stationdoes not Allow the UE Based Handover

As described above, the target base station may not support the UE basedhandover. As an alternative, the target base station may not allow theUE based handover due to its load or other reason(s).

For example, when the target base station does not allow the UE basedhandover, or when a preparing operation of the UE base handover isfailed while preparing the UE based handover, the target base stationmay transfer a handover preparation failure message to a source basestation. The target base station may transmit the handover preparationfailure message by including a cause value (e.g., non-admission for theUE based handover or a failure in the UE based handover) for this to thesource base station.

As another example, even when the target base station does not allow theUE based handover, the target base station may allow a typical networkbased handover. In this case, the target base station prepares ahandover by processing a handover request message from a source basestation according to a network based handover preparation procedure andgenerates an RRC message to be transferred to a UE for performing thehandover (for example, an RRCConnectionReconfiguration message includingthe mobilityControlInformation). Thereafter, the target base stationtransmits a handover request acknowledgment message to the source basestation. As an example, the handover request acknowledgment message orthe RRC message included in the handover request acknowledgment messagemay include indication information forresponding/acknowledging/indicating that the UE based handover has notbeen configured. As another example, the handover request acknowledgmentmessage or the RRC message included in the handover requestacknowledgment message may include indication information (e.g., set toa network based handover) for differentiating between the UE basedhandover and the network based handover. As further another example, thehandover request acknowledgment message or the RRC message included inthe handover request acknowledgment message may be configured andtransmitted only a network based handover request acknowledgment messageor an information element included in a handover request acknowledgmentmessage, without including information for differentiating the UE basedhandover.

Upon the receipt of the network based handover request acknowledgmentmessage through the handover request acknowledgment message or the RRCmessage included in the handover request acknowledgment message, thesource base station may transmit the received message to the UE. As analternative, for this, the source base station may transmit a handovercanceled message to the target base station and cancel the handover.

Upon the receipt of the RRC message included in the handover requestacknowledgment message from the source base station, the UE may performthe handover according to a network based handover procedure.

Like this, the source base station may verify whether the target basestation allows (e.g., support) the UE based handover, determine a typeof handover, and process a related procedure.

An Embodiment of Enabling a Target Base Station to Include and TransmitUE Based Handover Indication Information

A source base station may include handover preparation information in ahandover request message and then transfer the message including theinformation to the target base station. That is, the source base stationmay request a handover to the target base station according to aprocedure similar to the network based handover. In this case, thesource base station may not specify whether the handover request isbased on a UE or a network. Accordingly, when the target base stationreceives the handover request message, the target base station maydetermine a type of handover taking into account the situation of thetarget base station or capabilities of a UE.

For example, the handover preparation information in the handoverrequest message transferred from the source base station to the targetbase station may include capability information for the UE basedhandover. When the target base station supports a UE based handoverfunctionality, the target base station prepares a UE based handover. Forexample, the target base station generates UE configuration informationfor the UE based handover.

As another example, the handover request message or the handoverpreparation information in the handover request message transferred fromthe source base station to the target base station may include UE basedhandover request indication information as described above.

The target base station transmits a handover request acknowledgmentmessage to the source base station.

The handover request acknowledgment message is an RRC message forperforming the UE based handover and may be included in a container tobe transmitted to a UE. This container may include one or more of a newC-RNTI, a target eNB security algorithm identifier, a dedicated RACHpreamble, and target eNB SIBS. For example, the RRC message is an RRCreconfiguration message including the mobilitycontrolInfo. Such a RRCmessage is generated by the target base station and then transferred tothe UE through the source base station. The target base station mayadditionally include information for instructing the UE based handoverin an RRC message to be transmitted to the UE. As another example, thetarget base station may additionally include information for instructingthe UE based handover in a handover request acknowledgment message or anRRC message. For example, through this, the source base station mayindicate the UE based handover to the UE.

When the UE receives information instructing a UE based handover, the UEmay perform one or more of the following operations.

The UE maintains a connection with a source cell. The UE may requestscheduling to the source cell, or the scheduling may be indicated to theUE.

The UE stores a UE configuration/RRC context/RRC IE/L1, L2 configurationinformation for executing a handover to a target cell.

The UE performs measurement for a condition/event for determininghandover execution.

The target base station may generate and provide execution conditioninformation for the execution of the UE based handover. Hereinafter,information included in the execution condition information is describedin detail by being divided into event indication information, UEconfiguration information, and execution restriction information.

A Method of Enabling a Target Base Station to Indicate an Event forPerforming a UE Based Handover

For example, the target base station may include condition/eventconfiguration information for a UE based handover operation in ahandover request acknowledgment message or an RRC message. To do this, asource base station may add and transfer information for helping thetarget base station configure the UE based handover. For example, thesource base station may provide measurement configuration information ofthe source base station to the target base station. As another example,the source base station may provide event configuration information ofthe source base station to the target base station. As further anotherexample, the source base station may provide condition configurationinformation for the UE based handover to the target base station. As yetanother example, the source base station may provide RRM measurementresult(s) of the source base station to the target base station.Specifically, the source base station may provide RSRP/RSRQ/RS-SINRmeasurement result(s) of a candidate cell to the target base station. Asyet another example, the source base station may provide an eventreporting result of the source base station to the target base station.Specifically, the information provided to the target base station mayinclude measurement event related information including one or more ofan event at which a UE based handover request is triggered by the sourcebase station, whether reporting for each event has been performed or isrequired, a request time, an A3 event configuration, whether an A3 eventis satisfied, time-to-trigger information, mobility state information(t-hystnormal, t-evaluation, n-cellchangemedium, or n-cellchangehigh),UE cell change information and a UE based handover condition. As yetanother example, the source base station may provide event configurationinformation for UE based handover execution of the target base stationaccording to the suggestion of the source base station. For example, A3event information, or the like may be included in this.

A Method of Enabling a Target Base Station to Indicate UE ConfigurationInformation for Performing a UE Based Handover

For example, when the target base station satisfies a condition/eventfor the UE based handover in a handover request acknowledgment messageor an RRC message, the target base station may include UE configurationinformation for performing handover execution to a target cell bydisconnecting an existing connection with a source cell in the handoverrequest acknowledgment message or the RRC message, and then transfer tothe source base station.

A Method of Enabling a Target Base Station to Indicate Information forRestricting UE Based Handover Execution

As described above, in the UE based handover, a UE occupies a targetbase station resource until the UE determines handover is performed.However, it is undesirable for this situation to persist for a longtime. Accordingly, the target base station may indicate information forrestricting the UE based handover execution (e.g., a maximum waitingtime). For example, the target base station may indicate a timer valuefor indicating a validity period of handover execution. The UE receivinginformation indicating the UE based handover starts a timer forrestricting a validity period (a maximum waiting time) of the UE basedhandover execution. For example, when the UE based handover execution istriggered/initiated/determined/performed, the corresponding timer may bestopped. As another example, when the corresponding timer expires beforethe UE based handover execution istriggered/initiated/determined/performed, a condition/event for thehandover may be stopped. As further another example, when thecorresponding timer expires before the UE based handover execution istriggered/initiated/determined/performed, a target cell configurationincluding UE configuration information for performing handover executionmay be released.

An Embodiment of Enabling a Source Base Station to Include and TransmitUE Based Handover Indication Information

Unlike the embodiment described above, a source base station, not atarget base station, may configure information for indicating the UEbased handover and then transmit the configured information to a UE.

In the UE based handover, a UE may determine handover executionaccording to UE based handover configuration information (e.g., handoverexecution condition information) pre-configured under the control of abase station. In the UE based handover compared with the network basedhandover technology, handover commands may be issued faster; thus, it ispossible to reduce a handover failure. For example, in the network basedhandover technology, when a UE verifies that a specific event satisfiedto a measurement configuration occurs, the UE reports this to a basestation. Until the base station transmits a handover command to the UEthrough a handover preparation procedure with a target base station, incase a wireless environment suddenly changes due to blockage or thelike, there is a possibility that a handover may fail. However, in casethe UE based handover configuration has been instructed to the UE at anearlier time, the UE may trigger the handover execution withoutexperiencing a handover failure.

Accordingly, a source base station may configure information forinstructing a UE based handover to the UE.

When the source base station is allowed to provide the information forinstructing the UE based handover, the source base station may include aUE based handover configuration (e.g., handover execution conditioninformation, etc.) for one or more target base station(s) (targetcell(s)) in one RRC message, and then provide to the UE.

In this case, it is necessary for the source base station to include, inone RRC message, a UE based handover configuration for the target basestation/cell and a configuration for the target base station/cell, whichare differentiated from each other, and then provide it to the UE. Forexample, an RRC container/message/command/part/informationelements/indication information including a UE based handoverconfiguration for a target base station/cell, and an RRCcontainer/message/part/information elements/indication information forindicating by the source base station to the UE, which aredifferentiated from each other, may be included by the source basestation.

As another example, when the source base station includes a UE basedhandover configuration and a configuration for a source basestation/cell, which are differentiated from each other, in one RRCmessage, and then provides the RRC message to the UE, each of the RRCcontainers/messages/commands/parts/information elements/indicationinformation may include information (e.g., an index, an ID, anidentifier, a differentiated number, transaction ID, or the like) fordifferentiating from each other.

As further another example, when the source base station includes UEbased handover configurations for a plurality of target cellsdifferentiated from one another in one RRC message and then provides theRRC message to the UE, each of the RRCcontainers/messages/commands/parts/information elements/indicationinformation may include information (e.g., an index, an ID, anidentifier, a differentiated number, transaction ID, or the like) fordifferentiating from each other.

As yet another example, when the source base station is allowed toprovide the information for instructing the UE based handover, thesource base station may provide information for restricting one or morevalidity period(s) of UE based handover execution for one or more targetbase station(s) (target cell(s)). For example, to do this, the sourcebase station may instruct a timer value. When the UE receives theinformation instructing the UE based handover, the UE starts a timer forrestricting a validity period of the UE based handover execution. Forexample, when the UE based handover execution istriggered/initiated/determined/performed, the corresponding timer may bestopped. As another example, when the corresponding timer expires beforethe UE based handover execution istriggered/initiated/determined/performed, acondition/rule/regulation/event for the handover may be stopped. Asfurther another example, when the corresponding timer expires before theUE based handover execution is triggered/initiated/determined/performed,target cell configuration information (including UE configurationinformation) for performing handover execution may be released. As yetanother example, when the corresponding timer expires before the UEbased handover execution is triggered/initiated/determined/performed,the UE may transmit a message for canceling/releasing the UE basedhandover to the target base station.

When an RRC message including the information for instructing the UEbased handover is received, the UE may perform the UE based handoveroperations described above. As another example, the UE may transmit anRRC acknowledgment message to the source base station.

When an RRC message instructing a network based handover, which does notinclude the information for indicating the UE based handover, isreceived, the UE may perform typical network based handover operations.The UE may release all target cell configuration(s) for the UE basedhandover stored earlier.

As described above, the UE based handover for a plurality of target basestations or target cells may be instructed to the UE. In this case, whenthe UE performs the UE based handover relative to a specific target basestation or target cell, to prevent a resource from being wasted, the UEbased handover for one or more remaining target base station(s) ortarget cell(s) should be canceled. Hereinafter, related embodiments willbe described.

An embodiment of instructing the cancellation of a handover to one ormore remaining target base station(s) when a UE has completed ahandover.

In the UE based handover, UE based handover configuration(s) for one ormore target base station(s)/cell(s) may be instructed to a UE. Forexample, by a UE based handover request of a source base station, onetarget base station (for convenience of description, referred to as“first target base station”) may generate a UE configuration for a UEbased handover and provide the UE configuration to the UE via the sourcebase station. Thereafter, based on the reception of measurementreporting or any other reason, the source base station may request a UEbased handover to another target base station (for convenience ofdescription, referred to as “second target base station”) other than thefirst target base station, and then, the second target base station maygenerate another UE configuration for the UE based handover and indicatethis to the UE via the source base station.

In this case, as an example, when the UE configuration for the UE basedhandover by the second target base station is received, the UE mayrelease/discard the UE configuration for the UE based handover by thefirst target base station. That is, the UE may release first target basestation (first target cell) configuration information stored in the UEbased on information received earlier and store second target basestation (second target cell) configuration information based oninformation newly received. As an alternative, when determining the UEbased handover by the second target base station; when receiving aresponse in response to a UE based handover request from the secondtarget base station; or when indicating, to the UE, the UE configurationfor the UE based handover generated by the second target base station,the source base station may instruct the UE to cancel/release the UEbased handover preparation/configuration to the first target basestation.

As another example, even when the UE configuration for the UE basedhandover by the second target base station is received, the UE maymaintain the UE configuration for the UE based handover by the firsttarget base station and perform operations fortriggering/initiating/determining/performing UE based handover executionfor the second target base station.

As further another example, the source base station may requestrespective UE based handovers to both the first target base station andthe second target base station. The source base station may receiverespective UE based handover configurations from respective target basestations and provide the respective UE based handover configurations tothe UE through one RRC message.

When one or more UE based handover configuration(s) for one or moretarget cell(s)/base station(s) is/are instructed and when a handover toany one target cell/base station is completed, it is necessary torelease the handover preparation of remaining target cell(s)/basestation(s). To do this, when the source base station receives a handovercomplete indication (e.g., a UE context release message) from any targetbase station, the source base station may instruct thecancellation/release of the UE based handover to the remaining targetbase station(s).

As another example, when the UE performs operations fortriggering/initiating/determining/performing the UE based handover forany one target cell, or when satisfaction in a relatedcondition/rule/event is informed, the UE may release/discard acondition/rule/regulation/event for UE based handover execution for theremaining target cell(s)/base station(s) or UE configuration informationfor the UE based handover execution. A time point at which such anoperation is performed may be set to at least one of a time point atwhich a RACH is transmitted to a corresponding target cell, a time pointat which a random access preamble is transmitted, a time point at whicha random access response is received in the target cell, a time point atwhich random access is completed in the target cell, and a time point atwhich an UL signal is transmitted to the target cell, a time point atwhich synchronization is established with the target cell, a time pointat which a radio resource of the target cell is configured, and a timepoint at which an RRC confirmation message isinitiated/submitted/transmitted to the target cell. These time pointsmay be specified by the RRC connection reconfiguration message, orpre-configured.

As another example, when the UE leaves an RRC connected state due to aradio link failure, or the like, the UE may release/discard acondition/rule/regulation/event for UE based handover execution or UEconfiguration information for the UE based handover execution.

As another example, when the source basemodifies/changes/releases/re-indicates a UE based handover configurationfor a specific target cell, the UE may release/discard the UE basedhandover configuration stored/pending for the corresponding target cell.The source base station may indicate the cancellation/release of the UEbased handover to the corresponding target base station.

As another example, when the source base modifies/changes/re-indicates aUE based handover configuration for a specific target cell, the UE maystore the UE based handover configuration for the correspondingre-indicated target cell. When the source basemodifies/changes/re-indicates a UE based handover configuration for acorresponding target cell, the UE may replace a UE based handoverconfiguration for the corresponding re-indicated target cell with theearlier UE based handover configuration for the corresponding targetcell. For example, the UE may modify and store a target cellconfiguration for a target cell identical to the earlier stored targetcell to become the second target cell configuration according to thesecond high layer signaling.

As another example, when the source base stationmodifies/changes/indicates a configuration for a source cell, the UE mayapply the configuration of the source cell.

As described above, for performing the UE based handover, a source basestation or a target base station generates handover execution conditioninformation including UE configuration information, and the source basestation provides this to a UE. The UE may store target cellconfiguration information including UE configuration information usingthe received handover execution condition information and UE basedhandover command information and perform the UE based handover bymonitoring whether a condition is met or an event occurs without aseparate additional indication of the source base station. Discussionshave been conducted on various embodiments in cases where executioncondition information for a plurality of target base stations issimultaneously or sequentially received in the UE.

Through this, the UE is able to stably perform a handover to the targetbase station faster in the case of connection interruption that mayoccur due to any reason during the handover procedure.

Hereinafter, by focusing on all or part of embodiments or examplesdescribed above, the entire procedure of the UE based handover will bediscussed again with reference to the drawings.

FIG. 6 is a diagram illustrating a UE based handover procedure accordingto one embodiment of the present disclosure.

Referring to FIG. 6, a source base station 610 may perform a UE basedhandover procedure using handover execution condition informationgenerated by target base stations 620 and 630.

For example, the source base station 610 may transmit measurementconfiguration information for handover determination to a UE 600, atstep S610. The UE 600 measures radio channel quality for a target cellor a neighboring cell using the measurement configuration information,includes the measured result in measurement reporting, and transmits themeasurement reporting including the measured result to the source basestation 610, at step S615. The source base station 610 determineswhether to trigger a UE based handover taking into account themeasurement reporting information, UE capabilities, and the like, atstep S620.

When the UE based handover is determined to perform, the source basestation 610 transmits one or more handover request message(s) to thefirst target base station 620 and the second target base station 630 ifneeded, at steps S625 and S635. As described above, the handover requestmessage may include information representing whether the requestedhandover is the UE based handover and information for helping the targetbase stations 620 and 630 generate respective UE configurationinformation for the UE based handover. The first target base station 620or the second target base station 630 determines whether to allow the UEbased handover and transmits a handover request acknowledgment messageincluding execution condition information (including target cellconfiguration information, UE configuration information, and the like)to the source base station 610, at step S630 or S640.

The source base station 610 transmits, to the UE 600, an RRC connectionreconfiguration message including the execution condition information(including the target cell configuration information, the UEconfiguration information, and the like) received from the target basestations 620 and 630, at step S645. The RRC connection reconfigurationinformation may include at least one of UE based handover commandinformation and handover execution condition information. Further, asdescribed above, the RRC connection reconfiguration information mayinclude respective execution condition information for a plurality oftarget base stations, which is differentiated from one another.

The UE 600 stores the target cell configuration information anddetermines whether the UE based handover execution condition is metbased on a rule or an event of the execution condition information, atstep S650. In this case, when a restriction timer described above isoperated and a validity period has passed, the execution conditioninformation or the UE based handover command may be released. Whenhandover execution is determined to the first target base station 620,the UE 600 performs a handover procedure and an access procedure withthe first target base station 620 and transmits an RRC connectionreconfiguration complete message to the first target base station 620,at stop S655.

The first target base station 620 informs that the handover with the UE600 has been completed by transferring a handover complete message tothe source base station 600, at step S660. If needed, the source basestation 600 transmits a handover cancellation message to the second basestation 630 to prevent resources from being occupied unnecessarily, atstep S665.

FIG. 7 is a diagram illustrating a UE based handover procedure accordingto another embodiment of the present disclosure.

Referring to FIG. 7, a source base station 710 may directly configurehandover execution condition information to be transmitted to a UE 700.That is, without generating, by the target base station 720, a UE basedhandover request to a target base station 720 and execution conditioninformation (including UE configuration information) for the UE basedhandover in response to the request, the source base station 710 mayinstruct a UE based handover configuration to the UE according to adetermination of the source base station.

For example, the source base station 710 may determine whether totrigger a handover of the UE 700, at step S710. If needed, the sourcebase station 710 may determine whether to trigger the UE based handoverby receiving measurement reporting from the UE 700. As an alternative,the source base station 710 may determine the UE based handover withoutthe measurement reporting.

When the UE based handover is determined, the source base station 710transmits UE based handover configuration information to the UE 700, atstep S720. For example, the UE based handover configuration informationmay include UE based handover command information and handover executioncondition information described above. Further, this may be transmittedby being included in an RRC connection reconfiguration message.

When the UE 700 stores and configures UE based handover configurationinformation in the UE 700, the source base station 710 may receivehandover configuration complete information, at step S730.

Thereafter, the UE 700 determines whether to perform the UE basedhandover execution to the target base station 720 based on the handoverexecution condition information, at step S740. When the UE basedhandover execution is determined, the UE 700 may transmit an RRC messagerequesting the UE based handover to the target base station, at stepS750.

Hereinbefore, for more specific discussions, handover executioncondition information has been described as UE configurationinformation, target cell configuration information, target base stationconfiguration information, handover configuration information, or thelike; however, it should be noted that these terms denote a timer, anevent, a condition, a rule, a restriction/suppression information, orthe like needed for enabling a UE to perform the UE based handover. Theexecution condition information or all or each of these terms may denoteone parameter applied to all these terms. Alternatively, the executioncondition information or all or each of these terms may denote handoverexecution condition information itself. Accordingly, embodiments of thepresent disclosure are not limited to a specific term.

As described above, the UE based handover is efficiently performed inaccordance with embodiments of the present disclosure. Accordingly, itis possible to prevent resources of a target base station from beingwasted and to enable a UE to perform handover quickly and stably.

Hereinafter, configurations of the UE and the base station forperforming a part or all of embodiments described above will bediscussed with reference to the drawings.

FIG. 8 is a block diagram illustrating a UE according to at least oneembodiment of the present disclosure.

Referring to FIG. 8, the UE 800 performing a UE based handover mayinclude a receiver 830 configured to receive high layer signalingincluding UE based handover command information and handover executioncondition information for executing the UE based handover command from asource base station, and a controller 810 configured to store a targetcell configuration using the handover execution condition information.

The controller 810 may evaluate whether the handover execution conditioninformation is met and determine whether to perform a handover procedureto the target cell.

The receiver 830 may receive execution condition information includinghandover command information and condition information for executing thehandover command from a source base station having an RRC connectionwith the UE. As an example, the handover execution condition informationand the handover command information may be received by being includedin an RRC connection reconfiguration message.

A target base station may configure the handover execution conditioninformation and transmit the handover execution condition information tothe source base station. As another example, the source base station mayconfigure the handover execution condition information. For example, thehandover execution condition information may include a timer forindicating a validity period of the handover command or handoverexecution condition information. For example, when the timer expires,the handover command or handover execution condition information may beconsidered as invalid. In addition to this, the handover executioncondition information may include parameters, timers and the like,needed for determining whether to execute the UE based handover. Forexample, the handover execution condition information may include atleast one of parameter information for channel quality measurementneeded for performing the UE based handover, trigger conditioninformation for reporting a measured result, a timer for restricting orsuppressing measurement reporting, a timer for indicating the validityperiod, indication information indicating a UE based handover commandand UE configuration information for accessing a target base station.

The handover execution condition information or the handover commandinformation may be configured for each of a plurality of target basestations or a plurality of target cells. That is, the high layersignaling may include a plurality of handover execution conditioninformation or handover command information, each of which may beincluded in a container for each identifier or for each target cell ortarget base station.

For example, when UE based handover command information and handoverexecution condition information are received, the controller 810 mayverify whether the UE based handover is indicated and store the targetcell configuration according to the handover execution conditioninformation. For example, the controller 810 stores a measurementconfiguration for measuring channel quality of the target cell accordingto the handover execution condition information, and stores a triggerevent, a trigger condition, or the like applied to the target cell. Asanother example, when the UE configuration information included in thehandover execution condition information is stored and a handover to thetarget base station is determined, the controller 810 controls the UErapidly to attempt access to the target base station without separatelyreceiving a configuration of the target base station.

Meanwhile, as described above, when the handover execution conditioninformation includes a timer for indicating a validity period (orrestricting the applying of the validity period) of the handover commandinformation or the handover execution condition information, thecontroller 810 verifies whether the timer expires. When the timerexpires, the controller 810 may release the stored target cellconfiguration.

When a trigger condition included in the handover execution conditioninformation is met, the controller 810 may determine handover executionto the target base station controlling the corresponding target cell. Asan alternative, the controller 810 may not report a measurement resultfor the target base station to the source base station when the handoverexecution is determined. That is, when the UE based handover isconfigured, the controller 810 may control a measurement result meetinga handover execution condition not to be transmitted to the source basestation. As an alternative, when the UE based handover is configured,the controller 810 may control measurement reporting not to betransmitted to the source base station until the timer of the validityperiod expires.

When handover execution is triggered to the target base station, thecontroller 810 may perform a random access procedure and access thetarget base station using the UE configuration information describedabove. To do this, the transmitter 820 may transmit signals and dataneeded for accessing the target base station.

In addition, the controller 810 controls the overall operation of the UE800 needed for performing embodiments described above. Further, thetransmitter 820 and the receiver 830 may transmit or receive signals,messages, data required to perform embodiments described above to orfrom the source base station and the target base station.

FIG. 9 is a block diagram illustrating a source base station accordingto at least one embodiment of the present disclosure.

Referring to FIG. 9, the source base station 900 controlling a UE basedhandover procedure may include a controller 910 configured to generatehandover execution condition information for performing a UE basedhandover command, and a transmitter 920 configured to transmit highlayer signaling including UE based handover command information andhandover execution condition information to a UE.

When the handover execution condition information is changed, thetransmitter 920 may transmit, to the UE, second high layer signalingincluding changed handover execution condition information and UE basedhandover command information.

For example, the handover execution condition information may beconfigured by the source base station or be configured by the sourcebase station after the source base station has received information froma target base station. As an alternative, the source base stationreceives information to be included in the handover execution conditioninformation from a target base station and then generates the handoverexecution condition information to be transmitted to the UE.

The controller 910 may configure the handover execution conditioninformation or the handover command information for each of a pluralityof target base stations or a plurality of target cells.

The transmitter 920 may transmit execution condition informationincluding handover command information and condition information forexecuting the handover command to the UE having an RRC connection withthe source base station. For example, the handover execution conditioninformation and the handover command information may be transmitted tothe UE by being included in an RRC connection reconfiguration message.Further, the high layer signaling may include a plurality of handoverexecution condition information or handover command information, each ofwhich may be included in a container for each identifier or for eachtarget cell or target base station.

As described above, the UE may verify the high layer signaling receivedfrom the source base station and store a target cell configuration usingthe handover execution condition information. When a timer indicatingthe validity period is included in the handover execution conditioninformation, the UE may release the target cell configuration when thetimer which restricts the applying of the handover execution conditioninformation expires.

Further, the controller 910 may change to a network based handover, suchas the LTE handover procedure, after the UE based handover command hasbeen transmitted. As an alternative, the controller 910 may change atarget base station after a command of the UE based handover to aspecific target base station has been transmitted. In this case, thetransmitter 920 transmits second high layer signaling including changedhandover execution condition information and handover commandinformation to the UE

When the second high layer signaling is received, the UE may replace theearlier stored target cell configuration with a second target cellconfiguration using the handover command information and the handoverexecution condition information in the second high layer signaling.

In addition, the controller 910 controls the overall operation of thesource base station 900 needed for performing embodiments describedabove. Further, the transmitter 920 and the receiver 930 may transmit orreceive signals, messages, data required to perform embodimentsdescribed above to or from the UE and the target base station.

The standardized specifications or standard documents related to theembodiments described above constitute a part of the present disclosure.Accordingly, it should be construed that the incorporation of thecontent of the standardized specifications and part of the standarddocuments into the detailed description and claims is included withinthe scope of the present disclosure.

The forgoing has been presented to best explain the embodiments andexamples and thereby to enable any person skilled in the art to make anduse the invention as claimed. Various modifications, additions andsubstitutions to the described embodiments and examples will be readilyapparent to those skilled in the art without departing from the spiritand scope of the present disclosure. Therefore, exemplary aspects of thepresent disclosure have not been described for limiting purposes, but todescribe the embodiments, the therefore, the scope of the presentdisclosure shall not be limited to such embodiments. The scope of thepresent disclosure shall be construed on the basis of the accompanyingclaims in such a manner that all of the technical ideas included withinthe scope equivalent to the claims belong to the present disclosure.

CROSS-REFERENCE TO RELATED APPLICATION

If applicable, this application claims priority under 35 U.S.C § 119(a)of Patent Application No. 10-2017-0051258, filed on Apr. 20, 2017,Patent Application No. 10-2017-0051212, filed on Apr. 20, 2017 andPatent Application No. 10-2018-0043161, filed on Apr. 13, 2018 in Korea,the entire contents of which are incorporated herein by reference. Inaddition, this non-provisional application claims priorities incountries other than the U.S. for the same reason based on the KoreanPatent Applications, the entire contents of which are herebyincorporated by reference.

1-17. (canceled)
 18. A method of a user equipment (UE) for performing aUE based handover, the method comprising: receiving high layer signalingincluding UE based handover command information and handover executioncondition information for executing the UE based handover command from asource base station; storing a target cell configuration using thehandover execution condition information; and evaluating whether thehandover execution condition is met and determining whether to execute ahandover procedure to the target cell.
 19. The method according to claim18, further comprising: when the handover procedure is determined to beexecuted, executing the handover procedure; and when the handoverprocedure is executed successfully, releasing all handover executioncondition information configured for the UE and a configuration for ahandover candidate cell.
 20. The method according to claim 18, whereinthe handover execution condition information is configured for the UEthrough an A3 event by the source base station.
 21. The method accordingto claim 18, wherein the handover execution condition information isassociated with a measurement identifier identifying a measurementconfiguration.
 22. The method according to claim 18, wherein thedetermining whether to perform a handover procedure comprises:controlling a measure reporting operation for a handover execution eventnot to be triggered when the handover procedure is executed according tothe handover execution condition information.
 23. The method accordingto claim 18, wherein the handover execution condition information, aseparate handover execution condition is configured for each target cellor target base station.
 24. A method of a source base station forperforming a user equipment (UE) based handover, the method comprising:configuring handover execution condition information for performing a UEbased handover command; transmitting, to a UE, high layer signalingincluding handover execution condition information and UE based handovercommand information; and when the handover execution conditioninformation is changed, transmitting, to the UE, second high layersignaling including changed handover execution condition information andUE based handover command information.
 25. The method according to claim24, wherein the handover execution condition information is configuredfor the UE through an A3 event.
 26. The method according to claim 25,wherein when a handover procedure to the target cell is determined to beperformed, the UE performs the handover procedure to the target cell,and when the handover procedure to the target cell is executedsuccessfully, releases all handover execution condition informationconfigured for the UE and a configuration for a handover candidate cell.27. The method according to claim 24, wherein the UE determines whetherto execute a handover procedure to a target cell by evaluating whetherthe handover execution condition is met, and when the handover procedureis executed according to the handover execution condition information, ameasure reporting operation for a handover execution event is controllednot to be triggered.
 28. The method according to claim 24, wherein thehandover execution condition information, a separate handover executioncondition is configured for each target cell or target base station. 29.A user equipment (UE) for performing a UE based handover, the userequipment comprising: a receiver configured to receive high layersignaling including UE based handover command information and handoverexecution condition information for executing the UE based handovercommand from a source base station; and a controller configured to storea target cell configuration using the handover execution conditioninformation, wherein the UE determines whether to execute a handoverprocedure to the target cell by evaluating whether the handoverexecution condition is met.
 30. The user equipment according to claim29, wherein when the handover procedure to the target cell is determinedto be performed, the controller performs the handover procedure to thetarget cell, and when the handover procedure to the target cell isexecuted successfully, the controller releases all handover executioncondition information configured for the UE and a configuration for ahandover candidate cell.
 31. The user equipment according to claim 29,wherein the handover execution condition information is configured forthe UE through an A3 event by the source base station.
 32. The userequipment according to claim 29, wherein the handover executioncondition information is associated with a measurement identifieridentifying a measurement configuration.
 33. The user equipmentaccording to claim 29, when the handover procedure is executed accordingto the handover execution condition information, the controller controlsa measure reporting operation for a handover execution event not to betriggered.
 34. The user equipment according to claim 29, wherein thehandover execution condition information, a separate handover executioncondition is configured for each target cell or target base station.